Recently, in applications such as label package doubling as a protection of a glass bottle and a PET bottle etc. and display of articles, cap sealing, and accumulation package, there have been widely used drawn films (so-called heat-shrinkable films) composed of a polyvinyl chloride resin, a polystyrene resin, a polyester resin or the like. Of these heat-shrinkable films, a polyvinyl chloride film has problems that heat resistance is low, and it generates hydrogen chloride gas in incineration and causes dioxin. A polystyrene film has problems that it is inferior in solvent resistance, as well as an ink with a special composition needs to be used in printing, it requires high temperature incineration and generates a lot of black smoke accompanied by an abnormal odor in incineration. Therefore, as a shrink label, there has been widely used a polyester-based heat-shrinkable film which is high in heat resistance, easy to incinerate, and excellent in solvent resistance, and the use amount tends to increase being accompanied by an increase in distribution volume of PET containers.
As an ordinary heat-shrinkable polyester film, one which is allowed to shrink greatly in the width direction has been widely utilized. Although such a heat-shrinkable polyester film in which the width direction is the main shrinkage direction is subjected to drawing at a high ratio in the width direction in order to exhibit shrinkage properties in the width direction, with regard to the longitudinal direction orthogonal to the main shrinkage direction, there have been many cases in which the film is only subjected to drawing at a low ratio and there is also a case in which the film is not subjected to drawing. The film subjected to drawing only at a low ratio in the longitudinal direction and the film subjected to drawing only in the width direction have a drawback that the mechanical strength in the longitudinal direction is poor.
When the film is used as a label film for a bottle or a banding film for binding a box lunch container or the like, the film should be made into an annular form, mounted to the bottle or the box lunch container, and then allowed to heat-shrink in the circumferential direction. Therefore, when a heat-shrinkable film that heat-shrinks in the width direction is mounted as a banding film, after forming an annular-shaped member such that the width direction of the film is in the circumferential direction, the annular-shaped member should be cut into segments having a predetermined length, and each segment should be mounted to the bottle or the box lunch container, for example, by placing it by hand over the bottle or the box lunch container. Therefore, it is difficult to mount a label film or a banding film made of the heat-shrinkable film that heat-shrinks in the width direction to a bottle or a box lunch container at high speed. For that reason, recently, there is a need for a longitudinally heat-shrinkable film which can be wound around a bottle or a box lunch container directly from a film roll to mount the bottle or the box lunch container. With such a heat-shrinkable film, a center sealing step in which an annular-shaped member is formed and sealed or processing such as cutting, placing by hand, or the like can be eliminated, and thus mounting at high speed is also possible.
Furthermore, a film made of recycled raw materials derived from PET bottles is highly demanded in terms of environmental awareness. Since raw materials containing amorphous components in a large amount are used in an ordinary heat-shrinkable polyester film in order to impart heat shrinkage properties, the mixing rate of recycled raw materials is limited, and therefore it has not been possible to provide a heat-shrinkable polyester film containing recycled raw materials in a large amount. However, as described in Patent Document 1, it is known that a heat-shrinkable polyester film having sufficient shrinkage properties and high mechanical strength in the longitudinal direction as well as having small thickness irregularity in the longitudinal direction can be produced by contriving the drawing conditions even without using amorphous components in a large amount.
However, in the heat-shrinkable polyester film obtained by using raw materials which do not contain amorphous components in a large amount, the drawing stress at the time of drawing becomes high, and hence the stress at the time of shrinking, namely, the shrinkage stress becomes high. As a problem caused by a high shrinkage stress, for example, in the case of a label of a bottle in which after winding a film around the bottle, the end parts of the label are bonded to each other with an adhesive or the like and then the label is heated to finish shrinking, if the shrinkage stress is high, troubles such as displacement or separation of the bonded portion may occur. Moreover, in recent years, for the purpose of weight saving and waste reduction, containers with a small thickness are sometimes used as containers for box lunches and prepared foods, which are sold at convenience stores and supermarkets. The container with a small thickness decreases also in strength, and therefore if the shrinkage stress of a shrinkable film for packaging is high, a trouble of deformation of the container due to the shrinkage stress occurs.